1. Field of the Invention
The present invention relates to a power supply structure for a piezoelectric actuator that has a base member, a movable member, and a piezoelectric element arranged between the base member and the movable member and causes a shear deformation in response to a power applied state, as well as to a head suspension employing such a power supply structure.
2. Description of Related Art
Small-sized, precision information devices are rapidly advancing, and for use with such devices, needs for micro-actuators capable of conducting positioning control for very small distances are increasing. Such micro-actuators are highly needed by, for example, optical systems for correcting focuses and inclination angles, ink jet printers for controlling ink heads, and magnetic disk drives for controlling magnetic heads.
The magnetic disk drives are strongly expected to increase their storage capacities. Increasing the storage capacity of a magnetic disk drive is achievable by increasing the storage capacity of each magnetic disk in the magnetic disk drive. The storage capacity or recording density of a magnetic disk will increase, without changing the diameter thereof, if the number of tracks per inch (TPI) on the magnetic disk increases, i.e., if the width of a track narrows. For this, a magnetic head of a head suspension installed in the magnetic disk drive must conduct a precise positioning operation in a direction across the tracks, i.e., a sway direction. For realizing the precise positioning operation, an actuator capable of accurately moving and positioning the magnetic head within a very small section is needed.
To meet the need, Japanese Unexamined Patent Application Publication No. 2002-50140 proposes a head suspension for a disk drive. The head suspension includes a base plate, a connection plate having a hinge thinner than the base plate, a load beam provided with a flexure, and a piezoelectric actuator having a pair of piezoelectric elements.
This related art employs a dual actuator system that involves, for a precise positioning purpose, a voice coil motor and the piezoelectric actuator having two piezoelectric elements made of, for example, PZT (lead zirconate titanate).
The piezoelectric actuator in the dual actuator system minutely moves a front end of the load beam in a widthwise direction (sway direction) of the head suspension. Compared with a single actuator system employing only the voice coil motor, the dual actuator system employing the voice coil motor and piezoelectric actuator is capable of more precisely positioning a magnetic head attached to a front end of the head suspension.
The piezoelectric element described in the Japanese Unexamined Patent Application Publication No. 2002-50140 is of a compression type due to a deforming direction. On the other hand, Japanese Unexamined Patent Application Publication No. H10-293979 discloses a piezoelectric actuator employing a piezoelectric element of a shear type that demonstrates a shear deformation in response to a power supplied state when positioning a magnetic head.
An important issue for the head suspension employing the dual actuator system is how to supply power to the piezoelectric element. One approach to address the issue is disclosed in Japanese Unexamined Patent Application Publication No. H11-31368. To supply power to a shear type piezoelectric element, this related art forms a pair of wires on a base of a piezoelectric actuator and connects one of the wires to a first electrode of the piezoelectric element by wire bonding and the other wire to a second electrode of the piezoelectric element by wire bonding, as illustrated in FIG. 23 of the related art.
The wire bonding, however, applies local stress onto the piezoelectric element to secure bonding strength. The local stress onto the piezoelectric element tends to break the piezoelectric element. If the wire bonding is carried out moderately to prevent the breakage of the piezoelectric element, the bonding strength will be insufficient and deteriorate the reliability of electrical connection.
It is difficult for the related arts to prevent the breakage of a piezoelectric element, and at the same time, secure the reliability of electrical connection between power supply wiring and the piezoelectric element.